A recognized advantage of the diesel engine over spark-ignited gasoline engines is its high efficiency. The relative efficiency of the diesel engine over the spark-ignited gasoline engine is significant and translates directly to fuel economy and a lowering in greenhouse gas combustion byproducts such as carbon dioxide. On the negative side, however, the diesel engine suffers from the disadvantages of high particulate matter and NOx emissions. Particulate matter can be significantly lowered by blending oxygenates into the diesel fuel. These blends achieve significant reductions in particulate matter levels while not significantly increasing NOx. Unfortunately, common oxygenates that may be blended with a diesel fuel can exacerbate the formation of peroxide in the diesel fuel. Degradation of middle distillate fuel systems as a result of peroxides may be a serious problem at ambient storage and handling conditions.
There is also a current trend towards the use of ultra low sulfur diesel fuels, commonly referred to as fuels having 50 ppm sulfur or less (“ULSD fuels”). This trend toward the use of ULSD fuels has caused substantial combustion system changes and equally significant changes in fuel specifications. Many industrialized nations are reducing and/or have already reduced their mandatory maximum specifications for sulfur content. As a result, there are new concerns with respect to the performance and handling of the fuels formulated to meet the new specifications.
One concern with ULSD fuels is that the removal of sulfur compounds, some of which are effective peroxide scavengers and/or decomposers, may allow peroxides to build up in these fuels. The potential increase in peroxides is detrimental to fuel systems, because peroxides are known to degrade fuel system elastomers. The increase in peroxides, therefore, could cause the possible failure of seals, gaskets and hoses in a fuel system that uses ULSD fuels. See, for instance, Owen and Coley, Automotive Fuels Reference Book, Second Edition, 1995, pp. 520-523. The potential seriousness of this problem is also well documented in the problems with jet fuels in the 1960's and 1970's where high peroxide content in those fuels was associated with a high failure rate for fuel hoses, gaskets and seals in those systems. E.g., Fodor, et al., “Peroxide Formation in Jet Fuels,” Energy and Fuels, 1988, pp. 729-34.
Other concerns that arise when peroxide levels increase include fuel stability, color durability, and fuel sediments. These concerns are discussed generally in Bacha and Lesnini, “Diesel Fuel Thermal Stability at 300° F.,” Sixth International Conference on Stability and Handling of Liquid Fuels, Vancouver, Canada, Oct. 13-17, 1997; Vardi and Kraus, “Peroxide Formation in Low Sulfur Automotive Diesel Fuels,” SAE Paper No. 920826.